The present invention relates to conversion of gaseous alkanes to liquid hydrocarbons and, more particularly, in one or more embodiments, to a method and system that includes bromination of alkanes followed by conversion of the brominated alkanes to hydrocarbons wherein bromine recovery includes electrolysis.
Natural gas which primarily comprises methane and other light alkanes has been discovered in large quantities throughout the world. Many of the locales in which natural gas has been discovered are far from populated regions which have significant gas pipeline infrastructure or market demand for natural gas. Due to the low density of natural gas, its transportation in gaseous form by pipeline or as compressed gas in vessels is expensive. Accordingly, practical and economic limits exist to the distance over which natural gas may be transported in gaseous form. Cryogenic liquefaction of natural gas (LNG) is often used to more economically transport natural gas over large distances. However, this LNG process may be expensive and there are limited regasification facilities in only a few countries that are equipped to import LNG.
A number of techniques may be used to convert alkanes found in natural gas to liquids that may be more easily transported and, thus, generate additional value from natural gas. One technique for this conversion is a bromine-based process that may include bromination of alkanes to form brominated alkanes, and conversion of the brominated alkanes to hydrocarbons over an appropriate catalyst. An undesirable by-product from both the bromination and conversion steps in this process is hydrogen bromide. Before the hydrocarbons produced in this bromine-based process may be recovered as a liquid product, the hydrogen bromide may need to be separated from the hydrocarbons. The bromine may then be recovered from the hydrogen bromide and recycled within the process. In one instance, an aqueous technique may be used that includes scrubbing the hydrogen bromide from the hydrocarbon stream with an aqueous stream followed by neutralization of the dissolved hydrogen bromide to form a metal bromide salt. The metal bromide salt may then be oxidized to recover the bromine. In another instance, a dry technique may be used that includes reaction of the hydrogen bromide with a metal oxide to form a metal bromide salt, which may then be oxidized to recover the bromine.